1 Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota,Saint Paul, MN 55108, USA
2 Department of Food and Animal Sciences, College of Agricultural, Life and Natural Sciences,Alabama A&M University, Normal, AL 35811, USA; [email protected]
Simple Summary: The transition from late gestation to early lactation is a challenging period fordairy cows. A successful transition period depends on metabolic adaptation to the new physiologicalstate in early lactation and proper management in order to support the cow’s requirements. Thisreview paper will discuss various aspects of routine and consistent approaches to collect and analyzeherd records, to detect unintended disruptions in performance. In addition, we discuss how toincorporate methods to assess health, production, nutrition, and welfare information to monitor cowsduring the transition period. Lastly, we discuss management strategies that can be implemented toimprove the metabolic health and performance of transition dairy cows.
Abstract: The peripartum period of a dairy cow is characterized by several physiological andbehavioral changes in response to a rapid increase in nutrient demands, to support the final stagesof fetal growth and the production of colostrum and milk. Traditionally, the transition period isdefined as the period 3 weeks before and 3 weeks after parturition. However, several researchershave argued that the transition period begins at the time of dry-off (~60–50 days prior to calving)and extends beyond the first month post-calving in high producing dairy cows. Independent of thedefinition used, adequate adaptation to the physiological demands of this period is paramount for asuccessful lactation. Nonetheless, not all cows are successful in transitioning from late gestation toearly lactation, leading to approximately one third of dairy cows having at least one clinical disease(metabolic and/or infectious) and more than half of the cows having at least one subclinical caseof disease within the first 90 days of lactation. Thus, monitoring dairy cows during this period isessential to detect early disease signs, diagnose clinical and subclinical diseases, and initiate targetedhealth management to avoid health and production impairment. In this review, we discuss differentstrategies to monitor dairy cows to detected unintended disruptions in performance and managementstrategies that can be implemented to improve the metabolic health and performance of dairy cowsduring the transition period.
The transition period has traditionally been defined as the period 3 weeks before and3 weeks after parturition [1]. Nevertheless, metabolic changes can start earlier duringthe dry period and have long-term carryover effects post-calving. More importantly, anefficient transition into lactation is essential to ensure the success of dairy cows in currentproduction systems [2]. Despite this, ineffective adaptation to the new physiologicalstate remains common. The transition from late gestation to early lactation is the mostchallenging period for the dairy cow because of the rapid increase in nutrient demands to
support fetal growth and colostrum and milk production [3,4]. In early lactation, energydemands increase by about 300%, and calcium requirements are increased more than 65%to support lactogenesis [2–5]. At the same time, voluntary feed intake decreases to a levelthat is insufficient to cover the nutrient requirements of the cow, leading to a period ofdeficit in terms of both energy and major minerals [6]. Thus, homeorhetic and homeostaticadaptations are essential to coordinate the mobilization of lipid and mineral reserves duringthe transition period [7]. The pursuit of a more efficient production system has led thedairy industry to prioritize selection for milk yield over other traits, exacerbating thosemetabolic problems faced by dairy cows [8,9]. Therefore, dairy cows are at the greatest riskof developing disease(s) and involuntary culling during the periparturient period [10–13].
The routine and systematic collection and evaluation of information collected on-farmcan identify deviations from expected performance. Thus, monitoring can be used to detectunintended disruptions in performance under the existing management conditions or tomeasure the impact of an implemented intervention or change in management. When usedcorrectly, monitoring methods are extremely important to support management decisionsand can help motivate management or employee behavioral change on a dairy farm [14].Many approaches exist to monitor the transition dairy cow, and these approaches varydepending on the general goals of the farm. Therefore, choosing monitoring methods thatare practical and useful to address the problem(s) at hand is important.
The ideal monitoring methods, independent of the problems at hand, must: (1) have aminimum delay between causes and effect (lag); (2) not mask recent changes when usinghistorical data (momentum); (3) detect differences across the population (variation); and (4)not contain misleading information (bias) [14]. Unfortunately, it is not possible to achieveall these features using a single monitor, and a combination of monitoring methods isoften used to analyze the performance of transition dairy cows. In order to monitor thetransition period, the following broad areas can be used as a guideline: dairy herd generalinformation (e.g., stocking density, cow comfort, body condition scoring), milk productionduring early lactation, fresh cow health, and events (e.g., disease incidence and prevalence,death, and culling), and feeds and feeding (i.e., feeding management).
Considering the multifactorial nature of the pathogenesis of transition period diseasesand the delays in diagnosis and recording, herd-level monitoring and prevention strategiesrelying solely on the occurrence of a single disease as a standalone morbidity are practicallyimpossible and are of little significance to veterinarians, consultants, and dairy produc-ers [15]. Thus, carefully monitoring the transition dairy cow while considering all factorsaffecting health and performance enables prompt intervention to address rising problemsand enhances cow health, well-being, and productivity in a timely manner.
Considering the importance of the transition period for the success of dairy cows inintensive systems, this review article aims to describe the adaptations occurring during theperiparturient period and highlight strategies to improve cow performance and welfareduring the transition period. In addition, we aim to summarize management and treatmentstrategies to prevent the occurrence of metabolic diseases, potentially decreasing theeconomic cost of these diseases and improving cattle welfare.
2. Monitoring the Transition Dairy Cow2.1. Dairy Herd General Information
Appropriate stocking density—dependent on breed, parity, and lactation stage or dryperiod—is important to prevent negative effects on health and milk production in earlylactation. The stocking density during the far-off period should not exceed 100% of thetotal number of stall beds in free-stall housing systems. On the other hand, during theclose-up period, ideal stocking density varies according to breed. In a field trial evaluatingdry-cow feed additives, Holstein primiparous cows produced 0.72 kg per day less milk forevery 10% unit increase in stocking densities (based on headlocks) above 80% during theclose-up period [16]. Alternatively, 100% stocking density (based on headlocks) was notdetrimental in Jersey cattle. When comparing 80% versus 100% stocking densities, Silva
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and colleagues [17] reported no difference in the percentages of Jersey cows developingdiseases (48% vs. 45%, for 80% and 100% stocking densities, respectively) or being removedfrom the herd before 60 days in milk (8% for both groups). Non-significant differences werealso reported when investigating the innate immune response, body condition score (BCS),milk production, and reproductive performance [17]. Animals in the 80% stocking densitygroup, however, spent more time lying down near to parturition and were displaced fromthe feed bunk less often than cows in the 100% stocking density group [18]. Interestingly,cows in the higher stocking density group were less likely to start feeding within 5 min offeed delivery when compared to the cows in low stocking density pens [19]. In additionto behavioral changes, an increase in stocking density (9.7 m2 versus 19.3 m2 per cow)in the prepartum period was associated with lower hygiene scores [20]. Considering thepublished literature to date, there is enough evidence to advise against overstocking dairycows during the transition period.
In addition to appropriate stocking density, adequate heat abatement and comfortable,clean, dry, and appropriately designed stalls are essential to minimize stress during thetransition period. Adequate heat abatement during the dry period and after calving isimportant to minimize the effects of heat stress on milk production, reproductive perfor-mance, and the health of dairy cows [21–23]. For example, actively cooled nulliparous andmultiparous cows produce an extra 4 kg/d and 9 kg/d of milk, respectively, compared totheir non-cooled counterparts [21,24], likely because of the deleterious effect of heat stresson the mammary gland turnover during the dry period [25]. Moreover, heat stress duringthe dry period impairs the lifetime performance of dairy cows exposed to heat stress inuterus, with late gestation heat stress alone costing USD 371 million per year to the dairyindustry in the United States [26].
Appropriate stall design and bedding management improve cow use of the bed,improve lying time (up to 80 extra minutes in barns with the cleanest stalls) [27,28], decreaselameness and hock lesions [29], and consequently improve milk production [30]. In a largetrial in free-stall farms in Canada, a 10 kg increase in milk production was associated witheach one-point percentage increment in the proportion of dry stalls [31]. Comfortableand clean stalls are also important to keep dairy cows clean, decreasing the likelihood ofmetritis because of poor hygiene [32]. In general, the easiest method to assess cow comfortis simply to evaluate the cows’ behavior, their distribution pattern in the pen, and the useof the stalls [28,33,34]. When monitoring cow comfort, the “cows will tell us” the answers.Recommendations for management practices during the transition period are presentedin Table 1.
Body condition scoring is a simple, effective, and inexpensive monitoring parameter toassess the nutritional status of dairy cows throughout lactation. Various BCS systems havebeen described in different parts of the world using different scales [35,36]. Regardlessof scale, lower scores reflect thinner cows and higher scores reflect over-conditionedcows. During early lactation, a loss of BCS is expected as dairy cows are mobilizingtheir body reserves to support the increased nutrient demands of milk production. Livebody weight varies from 17 kg to 41 kg for each unit of BCS lost in primiparous andmultiparous Holstein-Friesian dairy cows, respectively [37,38]. As reviewed by Roche andcolleagues [39], changes in the body condition score in the transition period are expectedand can be used as a proxy to determine how dairy cows mobilize their body reserves tosupport the increased nutrient demands of the transition period. Ideally, BCS would beassessed at dry-off, calving, peak milk production (approximately 70 to 90 days in milk),and, when possible, once more during mid-lactation in order to monitor BCS dynamicsthroughout lactation, with an emphasis on the BCS dynamics in the transition period(dry-off, calving, and peak milk). Targeting a BCS at calving of 3.0 to 3.25 (on a five-pointscale) will maximize milk production, while decreasing the risk of metabolic and infectiousdiseases [40]. It is common for cows to lose between 0.5 to 1 point between calving and peaklactation. Losses of more than one point have been associated with impaired reproductiveperformance and should be avoided [41,42]. Cows that gained or maintained BCS during
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the dry period [42] or between 21d before and 21d after calving [43] also had fewer healthdisorders and improved performance compared to cows that lost BCS during the sameperiod. As soon as cows enter a period of positive nutrient balance (~9 weeks postpartum),they will replenish the body reserves depleted in the first third of their lactation. As a ruleof thumb, the BCS at dry-off (~12 months after calving) would be similar to the BCS atcalving, and, thus, cows should not lose or, likewise, gain much BCS during the dry period.Although we do not expect cows to gain excessive BCS during this period, dairy cows canincrease their BCS by 0.25 to 0.5-points during the dry period. As a result, best-practicewould dictate that a target BCS for cows at dry-off is set, and that this score is maintainedor only increased fractionally during the dry period to avoid obesity at calving [38,44].Target BCSs for the different stages of lactation are presented in Table 1. By consistentlymonitoring BCS, dairy producers, veterinarians, and nutritionists are able to determineif transition period nutritional management is optimal. This routine monitoring enablesthe identification of unexpected changes to BCS at different stages of lactation, in a timelymanner. If excessive loss or gain of BCS is observed, nutritional interventions can beadopted to address this finding.
Table 1. Recommended feeding, bunk management, and management practices during the transi-tion period.
Management Practice Goal
Removal of old feed from bunk DailyAvailability of feed >23 h/dayFeed push-up Every 4 hFeed refusal 3–5%Eating space >61cm/head (24 inches/head)Water availability >10 linear cm/head (4 linear inches/head)Stocking density 1
Far-off dry cows 100%Close-up dry cows 2 80–100%Fresh cow 80%Prepartum dry matter intakePrimiparous >10 kg/day (22 pounds/day)Multiparous >12 kg/day (26 pounds/day)Postpartum dry matter intakePrimiparuos >15.5 kg/day (34 pounds/day)Multiparous >19 kg/day (42 pounds/day)Social grouping Separate parity groupsAdditional cow comfort parametersHock scoring >80% of cows without hock lesionsBody condition scoreCalving 3.0–3.25Peak milk production (~70–90 DIM 3) 2.5–3.0Mid-lactation (~150 DIM 3) 3.0–3.25Dry-off 3.0–3.25Cow behavior >60% of lying cows chewing their cud 2 h after feeding
1 Stocking density calculated based on headlocks. 2 Recommended close-up dry cows sticking density variesdepending on breed and demographics of the pen. A lower stocking density (i.e., 80%) is beneficial for Holsteincattle and in herds where multiparous and primiparous animals are housed together. Higher stocking density(i.e., 100%) can be used in Jersey cattle herds without negative effects on health and performance postpartum.3 DIM = days in milk
2.2. Milk Production in Early Lactation
Monitoring milk production and milk composition during the first 2 to 3 months oflactation can be a useful tool to assess transition cow performance. Each dairy farm canestablish its own goal for peak milk production for an ideal cow that calved normally,received adequate diets, and did not develop any disease during the transition period,depending on her parity and breed. Unfortunately, monitoring milk production has many
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limitations, including a considerable lag between calving and peak milk production. The50 to 90 days between measuring the outcome (peak milk production) and fresh cow eventsis too long to enable prompt interventions to enhance a cow’s health and performance.Therefore, peak milk production should not be used as a standalone trait when monitoringmilk production, even though monitoring milk production during early lactation canhelp identify problems with cows during early lactation (i.e., less than expected milkproduction between 50 and 120 days in milk). In addition, this information can be usedto monitor whether peak milk production matches management expectations (Figure 1).Daily milk yield is a readily available and useful measure when monitoring transitiondairy cows, allowing for prompt changes to be made to address the problem(s) at hand [45].Early lactation milk production can be used as a proxy for the overall health of earlylactation dairy cows and, combined with other information gathered during monthly DairyHerd Improvement Association (DHIA) testing (i.e., parity, breed, previous 305-day milk,prior lactation length, month of calving, days dry, etc.), have been used to identify cowswith transition problems [45,46]. Decreased milk production in early lactation is stronglyassociated with disease development and culling by the 100 days in milk (DIM) [46,47].At the herd level, higher milk production in early lactation is associated with decreasedculling by the 60 DIM, when compared to herds with lower milk production in the sameperiod [12]. Unfortunately, the majority of dairy herds do not have equipment to measuredaily milk yield and rely on monthly testing.
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2.2. Milk Production in Early Lactation
Monitoring milk production and milk composition during the first 2 to 3 months of
lactation can be a useful tool to assess transition cow performance. Each dairy farm can
establish its own goal for peak milk production for an ideal cow that calved normally,
received adequate diets, and did not develop any disease during the transition period,
depending on her parity and breed. Unfortunately, monitoring milk production has many
limitations, including a considerable lag between calving and peak milk production. The
50 to 90 days between measuring the outcome (peak milk production) and fresh cow
events is too long to enable prompt interventions to enhance a cow’s health and perfor-
mance. Therefore, peak milk production should not be used as a standalone trait when
monitoring milk production, even though monitoring milk production during early lac-
tation can help identify problems with cows during early lactation (i.e., less than expected
milk production between 50 and 120 days in milk). In addition, this information can be
used to monitor whether peak milk production matches management expectations (Fig-
ure 1). Daily milk yield is a readily available and useful measure when monitoring tran-
sition dairy cows, allowing for prompt changes to be made to address the problem(s) at
hand [45]. Early lactation milk production can be used as a proxy for the overall health of
early lactation dairy cows and, combined with other information gathered during
ous 305-day milk, prior lactation length, month of calving, days dry, etc.), have been used
to identify cows with transition problems [45,46]. Decreased milk production in early lac-
tation is strongly associated with disease development and culling by the 100 days in milk
(DIM) [46,47]. At the herd level, higher milk production in early lactation is associated
with decreased culling by the 60 DIM, when compared to herds with lower milk produc-
tion in the same period [12]. Unfortunately, the majority of dairy herds do not have equip-
ment to measure daily milk yield and rely on monthly testing.
Figure 1. Milk production (kg; vertical axis) by days in milk (DIM; horizontal axis) for different
parity groups. The upper blue square highlights peak milk production between 60 and 120 DIM.
The lower red rectangle highlights problem cows (outliers characterized by low milk production,
compared with the rest of the herd between 50 and 120 DIM). Parity 1 (lactation = 1; blue dots),
Parity 2 (lactation = 2; red dots), Parity 3 (lactation > 3; green dots). Continuous lines represent the
average milk production for each parity group by days in milk.
Figure 1. Milk production (kg; vertical axis) by days in milk (DIM; horizontal axis) for differentparity groups. The upper blue square highlights peak milk production between 60 and 120 DIM.The lower red rectangle highlights problem cows (outliers characterized by low milk production,compared with the rest of the herd between 50 and 120 DIM). Parity 1 (lactation = 1; blue dots),Parity 2 (lactation = 2; red dots), Parity 3 (lactation > 3; green dots). Continuous lines represent theaverage milk production for each parity group by days in milk.
2.3. Fresh Cow Health and Events
The periparturient health of dairy cows is critical for their performance throughouttheir lactation [48,49]. More than 35% of all dairy cows, however, have at least one clinicaldisease (metabolic and/or infectious), and approximately 60% have at least one subclinicaldisease event during the first 90 DIM [50,51]. Hence, daily screening of fresh cows duringthe first 2 weeks of lactation, when possible, is recommended to identify cows presentingsigns of sickness. Monitoring disease events during the first few weeks of lactation providesuseful insights into how effectively transition period management supports cows duringthis challenging period. In addition, the type of disease provides us with information about
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the underlying metabolic and/or management problem(s) leading to the developmentof these diseases. Awareness of trends in the prevalence of diseases will often highlightproblems soon after they arise. The determination of herd alarm levels for incidence oftransition diseases is important when monitoring transition dairy cows. For this reason,appropriate use of a reliable and effective data recording system, from which reliable datacan be extracted, is paramount [15]. Table 2 summarizes the achievable prevalence levels,herd alarm levels, and disease costs (direct and indirect costs combined) per case for themost common diseases observed in dairy herds in the United States [15,52–54].
Table 2. Achievable and herd alarm levels and cost/case for the most common diseases observed indairy cows in the United States.
1 Cost per case was calculated based on direct (i.e., treatment, veterinary cost, etc.) and indirect (i.e., loss in milkproduction and impaired reproductive performance) cost based on Holstein confined herds in the United States.
Automated health monitoring systems generate alerts to warn farm managers aboutaltered activity and rumination time in dairy cows. These factors are indicative of a diseaseevent and thereby contribute to an improvement in labor resource allocation by enablingcaregivers to focus on dairy cows that that need to be examined and/or treated [55,56].Although the algorithms by which the different health monitoring systems generate healthalerts are not publicly available, independent researchers have validated several systemsdesigned to measure rumination time, activity (i.e., lying/resting and standing time),and heat detection. The majority of the literature available describes the validation ofwearable accelerometer sensor monitoring technologies (i.e., pedometers, collars, and eartag) indoors [55,57–59]. Nonetheless, the same technology has also been validated for usein grazing dairy cattle [60,61]. In general, the correlation between direct visual observation(gold standard) and each specific behavior recorded by the monitoring technologies ishigher in group-housed systems when compared to grazing systems. For instance, thePearson correlation coefficients for rumination are >0.97 in group housed animals [55,58]and 0.72 in grazing dairy herds [60].
In addition to identifying dairy cows that need attention at the time of the diseaseevent, automated health monitoring systems can detect changes in dairy cow activityand rumination time prior to the onset of the disease event [62]. Automated healthmonitoring systems have been shown to effectively identify dairy cows that will havea retained placenta [63], hypocalcemia [62], metabolic and digestive disorders [64–66],metritis and pneumonia [67], ketosis [68,69], and development of hoof lesions [70,71],before the diagnosis of the disease by farm personnel. Recently, Sahar and colleagues [72]reported that cows that spent less time eating during the prepartum were more likely tobe diagnosed with metritis and hyperketonemia after calving. In this experiment, cowswere continuously observed for 90 min immediately after fresh feed delivery every otherweek during the 8 weeks prepartum, with every additional 15 min spent eating during the90-min interval increasing the odds of a cow remaining healthy by 1.3 times [72]. Similarly,cows that remain healthy post-calving spend 14% more time ruminating pre-calving thancows that developed metritis and hyperketonemia after calving [73]. In a series of reports,Stangaferro and colleagues reported that automated health monitoring systems couldidentify cows that develop metabolic and digestive disorders [64] and those that developsevere cases of metritis [66] 5 days before this could be achieved by farm personnel.
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The scientific body of evidence regarding the association between peripartum diseaseand measurable changes in periparturient physical activity [74], in addition to the growingchallenge of hiring workers, is likely to increase the adoption of automated monitoringsystems in routine dairy operations. The value of early detection of disease onset usingautomated monitoring systems is gaining wide acceptance and is contributing to improve-ments in health outcomes. However, quantifying the economic benefits of using thesesystems for farm managers and producers is challenging, as this value is dependent onspecific characteristics of each dairy operation and the technology used. An economic anal-ysis based on stochastic models, determined that investing in precision dairy technology isa positive economic decision when this technology improves estrus detection and earlydisease detection [75]. Similarly, investment in automated activity monitoring technologiesis not only worthwhile, but also contributes to farm profitability [76].
Although procedures and protocols are used in the prevention, early detection, andtreatment of diseases of dairy cows, these health events occasionally go unresolved, leadingto the departure of cows from the herd for sale, slaughter, salvage, or death [11]. Cullingand mortality of cows during the first 60 DIM is strongly associated with metabolic dis-eases characteristic of the transition period [13,77]. As expected, premature culling ordeath of dairy cows results in substantial economic losses to the dairy industry and is animportant cow welfare issue [78]. It is very important to consistently record the reasonswhy cows leave the herd in order to recognize trends that may be used to identify areas toimprove transition cow management. The majority of cows leave the herd before dying,and the definition of voluntary and involuntary culling can be confusing. However, keep-ing good records of the causes of death for the animals that die within each herd can beextremely valuable when investigating current management strategies and determiningfuture directions for management changes that are necessary to improve health and perfor-mance. Standardized post-mortem examination and reporting (i.e., death certificates) havebeen suggested as a reasonable approach to gather reliable information to be used wheninvestigating the management of the dairies [79].
2.4. Feeds and Feeding
The primary goal of good transition cow nutrition management is to deliver a well-balanced diet to meet, but not exceed, the nutritional requirements of the cow. It isimportant for farmers, veterinarians, and nutritionists to routinely monitor cows’ rationsas they are delivered to the cows to determine if the feed delivered to the cows on a dailybasis matches the recommended diets for each particular group of cows. In addition,monitoring the feed bunk between feed deliveries and the number of refusals just beforethe subsequent feeding, is important to gather information about sorting, feed push-upfrequency, and if the ration delivered is consistent with the diet designed by the nutritionist.Altogether, this information is important to determine the management adjustments thatare required to maximize dry matter intake and, consequently, decrease the likelihood ofdisease development and improve milk production.
The number of animal groups receiving differently formulated diets within the lacta-tion cycle is determined by the herd size. Separating lactating and non-lactating animalsinto multiple groups is challenging in smaller herds. Thus, smaller herds often only havea lactating and non-lactating diet. By contrast, larger herds can have up to five differentfeeding groups: high (early lactation), medium (mid-lactation), low (late lactation), far-off(first 30 days of the dry period), and close-up (last 30 days before calving). Although differ-ent herds, depending on convenience, can implement different grouping combinations, atwo-stage feeding strategy throughout the dry period is recommended. The two-stage feed-ing strategy is associated with increased fat yield and 3.5% fat-corrected milk productionduring the first 5 months of the subsequent lactation [80]. Moreover, the implementation ofa two-stage feeding strategy during the dry period (far-off and close-up dry cows) enablesthe formulation of diets with feed additives and anionic salts to prevent metabolic diseases
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around parturition. These strategies are further discussed in the next section of this review.The recommended nutritional management practices are presented in Table 1.
3. Improving Metabolic Health of the Transition Dairy Cow
Management strategies to facilitate an efficient transition into lactation are essentialfor the success of any approach used to improve the health and production of dairy cows.For example, the proper nutritional management of dairy cows during the late stagesof the previous lactation and the dry period can decrease the prevalence of metabolicdisorders (i.e., hypocalcemia, ketosis, displaced abomasum, and fatty liver) during earlylactation [81–83].
3.1. Prevention of Mineral Disorders: Hypocalcemia
Nutritional strategies are commonly used to prevent clinical hypocalcemia [81,84–87].The use of anionic salts to create a negative dietary cation–anion difference (DCAD), causesa drop in blood pH that results in low-grade calcium release from the bones into the extra-cellular fluid in order to balance the excessive concentration of anions in circulation [88].The mobilized calcium is excreted by the kidneys until parturition, when it is then usedto meet the elevated milk calcium demands of lactation [4,89]. Therefore, the beneficialeffects of negative DCAD diets, fed during the dry period for early lactating dairy cows,are explained by an enhanced capacity to mobilize calcium from the bones and the mainte-nance of parathyroid hormone actions. The optimum DCAD value for prepartum dietshas not been established [90,91]. A recent meta-analysis indicated that prepartum DCADdoes not need to be less than negative 150 mEq/kg of dry matter [91]. It is important tohighlight that different anionic salt sources will determine different levels of metabolicacidosis. In their seminal work, Goff and colleagues [92] demonstrated that sulfate saltshave approximately 60% of the blood acidifying activity of chloride salts, suggesting thatthe addition of chloride salts is more effective in inducing metabolic acidosis than sulfatesalts. Different anionic salts also lead to different reductions in dry matter intake, eventhough the DCAD level in the diet formulation is equal [91]. Because the decrease in DMIis mainly mediated by the metabolic acidosis caused by the feeding of acidogenic diets [93],monitoring metabolic acidosis when feeding anionic salts during the pre-fresh period isextremely important. The degree of acidification caused by use of anionic salts during thedry period can be determined by measuring individual cow urine pH, with optimal urinepH of dairy cattle consuming anionic salts during the dry period being between 5.5 and6.2 [94]. It is important to reinforce that cows should be consuming anionic salts for at least2 days before assessing their effect on urine pH.
The strategy of adding anionic salts to the pre-calving diet to improve calcium home-ostasis around parturition and prevent milk fever was first described 50 years ago [95].Since then, many groups have replicated these results using different anionic salts andDCAD targets [96–98]. Diets with limited calcium concentrations (0.4% of dry matter) havetraditionally been used in the formulation of acidogenic prepartum diets. Recently, Leanand colleagues [99] reported a significant decrease (risk ratio = 0.60) in clinical hypocal-cemia, in addition to a 1.1 kg/d increase in milk production by multiparous dairy cowsthat were fed DCAD diets pre-calving. Similarly, in a recent meta-analysis of 41 previouslypublished experiments, Santos and colleagues [91] determined that, when the postpartumDMI increased 1 kg/d, the predicted incidence of clinical hypocalcemia was reduced from11.7 to 2.8%, and the number of disease events per cow was decreased by 50% whenprepartum DCAD was reduced from 200 to −100 mEq/kg. The results from the samemeta-analysis suggest that the odds of having clinical hypocalcemia increases 1.8-fold foreach percentage unit increment in the dietary calcium content (e.g., from 0.4 to 1.5%) [91].Despite these results, postpartum blood calcium concentrations and health outcomes werenot different when dairy cows were fed acidogenic diets (−240 mEq/KG of dry matter)with low (0.4% of DM) or high (2.0% of DM) dietary calcium concentrations [100]. Thissuggests that the addition of calcium to acidogenic diets does not negate the effect of
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the compensated metabolic acidosis triggered by the anionic salts. Furthermore, resultsfrom recent investigations showed that adding calcium to fully acidified diets improvedpostpartum uterine health and fertility, highlighting the importance of calcium metabolismfor uterine immunity [101]. Hence, further investigation is needed in order to determinethe ideal DCAD and calcium concentration in pre-calving acidogenic diets.
Another nutritional strategy that has been investigated to prevent hypocalcemia isthe incorporation of compounds capable of biding dietary minerals, including calcium,decreasing the availability of calcium for intestinal absorption. The addition of syntheticzeolite A to non-acidified prepartum diets resulted in improved serum calcium concentra-tions around parturition and similar postpartum performance, when compared to animalsreceiving a similar base diet without the addition of calcium binders [102]. However, fewpeer-reviewed articles have investigated this strategy.
Nutritional management of dairy cows during the dry period has been the key todecreasing the incidence of clinical cases of hypocalcemia to levels as low as 1% [103].Nonetheless, the prevalence of subclinical hypocalcemia is high in the US, with as manyas 73% of animals of parity ≥3 experiencing low blood calcium concentrations duringthe first 3 DIM [104,105]. Combining the severity and duration of the low blood calciumconcentration bouts in early lactation, might represent a better parameter to understandthe association of low calcium concentrations in the first few days post-calving and animalhealth and performance compared to the alternative method of checking blood calciumconcentration with a single sample within the first 24 h of calving [106,107]. When usingthis approach, McArt and Neves (2020) reported that 17.4% of primiparous and 19% ofmultiparous cows had transient hypocalcemia (low calcium concentrations in the first daypostpartum), whereas 23% of primiparous and 13% of multiparous cows had persistenthypocalcemia in early lactation (continuously low calcium concentrations extending be-yond the first day postpartum). Furthermore, transient subclinical hypocalcemia has beenassociated with elevated milk production, whereas persistent subclinical hypocalcemia hasbeen associated with decreased milk production, increased risk of early lactation diseaseand culling, and impaired reproductive performance [106,107].
Prophylactic use of oral calcium supplementation during early lactation has beenproposed as a strategy to overcome calcium deficits during the first few days of lacta-tion, especially for subclinical hypocalcemia cases. Unlike intravenous administration ofcalcium, oral calcium boluses establish a more sustained elevation of blood calcium concen-tration without elevating blood calcium concentrations to near cardiotoxic levels [108,109].Calcium supplementation immediately after calving has been shown to increase polymor-phonuclear leukocyte function [110]. Oral calcium supplementation decreased the risk ofone or more health disorders (i.e., retained placenta, displaced abomasum, metritis, andmastitis) by 15% in parity ≥3 cows, with low blood calcium concentrations being notedpostpartum [111]. Furthermore, a stochastic analysis determined that the best return oninvestment (1.8 ± 0.8) and the greatest average net impact (USD 8313 ± 3540) was obtainedwhen high previous lactation milk yield cows and lame cows received supplementationwith calcium bolus post-calving [53]. Nonetheless, very few benefits are associated withblanket supplementation of fresh cows with oral calcium, and some evidence indicates thatoral calcium supplementation is not recommended for primiparous cows [53,111,112].
3.2. Prevention of Excessive Energy Imbalances: Hyperketonemia and Fatty Liver
Different nutritional strategies are used to minimize energy deficits and excessivelipid mobilization during early lactation. Excessive energy deficits remain a common issue,however, leading to the occurrence of metabolic diseases [15]. In an effort to decreaseeconomic losses associated with the negative downstream outcomes following elevatedconcentrations of blood beta-hydroxybutyrate (BHB) during early lactation, a combinedtesting-and-treating strategy has been suggested [83]. This strategy consists of testingapproximately 20 cows, every other week, between 3 and 14 DIM, for blood BHB concen-trations, using a cow-side test. Cows with BHB concentrations ≥1.2 mmol/L are deemed
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to be positive for hyperketonemia. This categorization does not group dairy cows intosubclinical and clinical ketosis, but rather into moderate (BHB between 1.2 mmol/L and2.9 mmol/L) and severe (BHB ≥ 3.0 mmol/L) hyperketonemia cases based only on theblood BHB concentration, independent of other clinical signs associated with ketosis. Thefrequency of hyperketonemia determines the recommended intervention. A herd preva-lence of <15% warrants monitoring. If a 15 to 40% prevalence is detected, all cows should bemonitored twice between 3 and 9 DIM and all positive individuals should be treated with300 mL of propylene glycol for 5 days. If more than 40% prevalence is detected, all cowsshould be treated with propylene glycol starting at 3 DIM, for 5 days. Hyperketonemiccows treated with propylene glycol are 40% less likely to develop displaced abomasa thantheir non-treated counterparts [83]. Herds with an elevated hyperketonemia prevalenceshould revise management and nutritional protocols to achieve acceptable prevalence rates,and disease prevalence should be re-assessed after 1 month [113,114]. Recently, severalgroups have investigated the use of monthly test-day information [115], Fourier transforminfrared spectrometry [116], on-farm cow data [117], and multiple biomarkers of metabolicstress [118] to predict the occurrence of hyperketonemia and other metabolic diseases.These strategies have the potential to identify dairy cows at risk of health disorders postpar-tum during the dry period and, in some cases, at dry-off. Early identification of individualcows, or groups of cows, that have a higher risk for the development of metabolic diseasespostpartum is important for timely intervention to prevent the occurrence of these diseases.
Several other nutritional and management strategies have been tested to treat, prevent,or alleviate fatty liver disease with limited success. Increasing the nutrient density oftransition diets to increase propionate production in the rumen, as well as supplementingdietary fat to increase the dietary energy density were strategies proposed to preventfatty liver [119]. Nonetheless, increasing the energy density of prepartum diets had littleeffect on the liver accumulation of triglycerides after calving [120]. In fact, overfeedingenergy to dairy cows during the dry period (150% of energy requirement; 1.62 Mcalof net energy for lactation (NEL)/kg of dry matter (DM)) was associated with greatermobilization of triacylglycerol from adipose tissue, increased concentrations of BHB, andgreater concentrations of lipids in the liver during the postpartum period, when comparedto dairy cows fed to meet energy requirements (100% of energy requirements; 1.21 Mcal ofNEL/kg of DM) [121]. Similar results were reported in a recent study that also compareddifferent planes of nutrition (150% versus 100% of energy requirement) during the last28 days prior to parturition [122]. Taken together, these findings support the use ofcontrolled energy diets to minimize energy deficits postpartum. Feeding controlled-energydiets with adequate physical format, limits the energy intake before parturition to meetenergy requirements, while both preventing BCS gain and diminishing the extent of thepostpartum energy deficit [123]. The use of controlled-energy diets during the dry periodleads to a better transition, a decrease in the occurrence of health problems, and improvesdairy cow performance [123].
Feed additives that decrease adipose tissue lipolysis (e.g., propylene glycol, monensin,chromium, and niacin), enhance hepatic very low-density lipoprotein secretion (e.g., cholineand methionine), and alter hepatic fatty acid metabolism (e.g., carnitine and tallow),have been suggested as nutritional strategies to prevent and treat fatty liver. Among thedietary supplements tested, only choline and propylene glycol repeatedly reduced livertriglycerides. The role of nutraceuticals during the transition period of dairy cows has beenreviewed by Lopreiato and colleagues [124] elsewhere. Management strategies such asfeeding one diet during the entire dry period and shortening the dry period have beenproposed, but the current available data are insufficient to assess the effectiveness of suchstrategies in reducing lipid accumulation in the liver [82].
3.3. Metabolic Health and Infectious Diseases
Elevated concentrations of blood BHB and non-esterified fatty acids (NEFA) as wellas decreased concentrations of blood calcium, are characteristic of an unsuccessful tran-
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sition from late gestation to early lactation and have been associated with an increasedrisk of many diseases, including infectious diseases, such mastitis [125] and uterine dis-eases [49,107,126–128]. Elevated concentrations of ketone bodies decrease neutrophilfunction [129–131] and are associated with increased oxidative stress [132]. Similarly,hypocalcemia is associated with impaired neutrophil function [133,134]. Thus, metabolicdiseases are risk factors for infectious diseases as they predispose cows to the developmentof infectious diseases. Although this review focusses on the metabolic diseases that occurduring the transition period, it is important to highlight that the inadequate adaptation tothe increased nutritional demands of the transition period can increase the susceptibility ofthe dairy cows to infectious diseases. Pathogenesis, management, and strategies to preventand treat mastitis and uterine diseases have been recently reviewed by Ruegg [135] andGilbert [136], respectively.
3.4. Additional Management Practices to Improve Health of the Transition Cow
Improving cow comfort during the transition period has a remarkable impact on drymatter intake and, in turn, improves the welfare, health, and performance of dairy cowsduring early lactation. Aspects such as proper stocking density, sufficient bunk space,access to water, correct stall designs, comfortable and sanitary bedding material, heatabatement systems, and frequent and adequately delivered feed should not be overlooked.Future studies to establish physiological limits considering the specific best managementconditions, will potentially yield data that can be beneficial in detecting health problemsduring early lactation in dairy cows. When possible, managing cows in a transition orfresh cow pen in the first few weeks postpartum, facilitates the monitoring of metabolicand infectious diseases, enabling farmers, veterinarians, and nutritionists to act quicklywhen problems arise.
The importance of adequate feeding strategies has been highlighted several times inthis review. In order to accomplish these goals, comprehensive total mixed ration (TMR)audits, when feeding TMRs, should be performed on a regular basis to determine if thefeed delivered to the cows on a daily basis is in accordance with the recommended dietfor each particular group of cows. Methods to evaluate TMR consistency and practicalsolutions to improve TMR quality to enhance production and health in dairy farms havebeen described by Oelberg and Stone [137].
4. Conclusions
The transition period is challenging for both cows and producers. Efficient transitioninto lactation is essential to maintain health and achieve expected production performances.The establishment of routine and consistent systems to collect and analyze herd recordsis essential to detect unintended disruptions in performance. Many approaches exist formonitoring the transition program in a dairy herd, but it is not practical to use all of themeasures available. Identifying each dairy farm’s unique transition health challenges willfacilitate the selection of the most practical and useful aspects that require monitoring on aregular basis, thus simplifying the monitoring task. Gathering general information regard-ing the dairy herd, monitoring milk production during early lactation, establishing effectivemanagement strategies to prevent and record fresh cow health events, and understandingfeeds and feeding are broad areas that need to be further investigated when monitoring thetransition program. Moreover, implementation of best management practices for transitioncows will substantially improve the metabolic health and immune functioning of cows,resulting in improved cow welfare, health, and production.
Author Contributions: Conceptualization, L.S.C. and B.O.O.; writing—original draft preparation,B.O.O.; writing—review and editing, L.S.C. All authors have read and agreed to the publishedversion of the manuscript.
Funding: The authors of this review article received no external funding.
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Acknowledgments: The authors would like to thank Rafael Bisinotto for challenging us to organizeour ideas regarding this topic for this review and Elise Shepley for kindly reviewing and editing themanuscript prior to final submission.
Conflicts of Interest: The authors declare no conflict of interest.
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